Field of the Invention
The invention relates to a method of supplying or feeding dampening solution to a printing form of an offset printing press.
In offset printing with offset printing presses, it is necessary to feed ink and dampening solution to the printing form. This is accomplished with so-called inking and dampening units, respectively. The dampening solution is preferably treated water, mixed with dampening-solution additives as well as a share of alcohol. An arrangement of rollers in the dampening unit ensures that the dampening solution is applied to the printing form in as uniform a distribution as possible in order to form a thin dampening-solution film. Particularly considering the present-day striving for increased productivity in printing and the use of less-experienced pressmen, it is becoming ever more important that the production process should be stable, simple and problem-free. One of the dreaded troubles is so-called emulsification in the inking unit, which may occur particularly in the case of unevenly structured printing subjects and/or lengthy production processes. It has become known heretofore that, even if the sheet is completely printed with ink, the conventional offset printing process requires a component or share of dampening solution. This is, for example, because of the non-printed margins and, also, in order to stabilize the transfer process. The quantity of dampening solution required therefor is relatively large. In contrast therewith, non-printed image areas require a smaller component or share of dampening solution. If printing is performed with the same subject over a lengthy period of time, it is then possible for problems to occur, as shown in practice; in particular, the aforementioned emulsification may occur, the only recourse to which then being the time-consuming cleaning of the inking unit. The production process becomes particularly sensitive when only small areas or even just lines are being printed.
Published Non-prosecuted German Application 40 28 083 discloses a method of controlling dampening in offset printing presses wherein, during the production run, the smear limit is reached at intervals, with the actual value measured at the smear limit being used as the setpoint value for the following controlling of the quantity of dampening solution.
It is accordingly an object of the invention to provide a method of feeding dampening solution of the foregoing general type, which avoids emulsification in the inking unit, particularly in the case of unevenly structured subjects and/or lengthy production processes.